Polyethylene (PE) resin has been used for the manufacture of pipes for the transport of fluids such as gases and liquids since the 1970's. The widespread use of polyethylene in pipe applications is due to the lightweight properties, strength, flexibility and chemical stability of the polyethylene material.
High performance polyethylene resins such as PE 80 and PE 100 resin have been developed for the production of pipes with improved resistance to slow crack growth and rapid crack propagation. Accordingly, such polyethylene resins can be used in the formation of pipes where high strength is required, such as in pipes that are pressurised during normal use. However, while PE 80 and PE 100 resins possess a number of favourable mechanical and physical properties, there remains a need to develop new polymer materials that are capable of forming pipes having one or more improved properties.
It is currently possible to make pressure pipes with a minimum required strength of 10.0 MPa using PE100 materials. A stronger PE material, suitable for pressure pipes with a minimum required strength of 11.2 MPa (PE112) or 12.5 MPa (PE125) would be very desirable. In general it has been found that attempts to prepare PE materials for pressure pipes of higher resistance to internal pressure have led to other properties, particularly toughness, processability and slow crack growth, being significantly reduced. For example, commercially available PE composition for pipe have been prepared to optimise minimum required strength (MRS) to 11.2 MPa and 12.5 MPa but the increase in resistance to internal pressure has led to brittle failures, particularly at temperatures of 60° C. and 80° C.
In other instances, the addition of particulate matter such as mineral fillers to polyethylene to improve strength and load bearing performance have typically culminated in degradation of the toughness and ductility of the composite.
A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.